Method for forming patterned electrically conductive transparent coating including fused metal nanowires

Abstract

Polymer binders, e.g., crosslinked polymer binders, have been found to be an effective film component in creating high quality transparent electrically conductive coatings or films comprising metal nanostructured networks. The metal nanowire films can be effectively patterned and the patterning can be performed with a high degree of optical similarity between the distinct patterned regions. Metal nanostructured networks are formed through the fusing of the metal nanowires to form conductive networks. Methods for patterning include, for example, using crosslinking radiation to pattern crosslinking of the polymer binder. The application of a fusing solution to the patterned film can result in low resistance areas and electrically resistive areas. After fusing, the network can provide desirable low sheet resistances while maintaining good optical transparency and low haze. A polymer overcoat can further stabilize conductive films and provide desirable optical effects. The patterned films can be useful in devices, such as touch sensors.

What is claimed is: 
     
         1 . A method for forming a patterned electrically conductive transparent coating, the method comprising:
 applying a metal nanowire fusing solution to a patterned initial coating layer on a substrate to form a patterned differentially conductive coating having regions with a sheet resistance of no more than about 270 ohms/sq and regions having a sheet resistance of at least about 20,000 ohms/sq, wherein the fusing solution comprises a fusing agent, and wherein the patterned initial coating layer comprises regions of metal nanowires and uncrosslinked radiation curable polymer and other regions of metal nanowires and crosslinked polymer, wherein the fusing solution converts at least a portion of the metal nanowires and uncrosslinked radiation curable polymer into a fused metal nanostructured layer with a sheet resistance of no more than about 270 ohm/sq.   
     
     
         2 . The method of  claim 1  wherein the applying of the metal nanowire fusing solution comprises coating the solution over an entire surface of the patterned initial coating layer. 
     
     
         3 . The method of  claim 1  wherein the substrate comprises, and the patterned differentially conductive coating has an optical transmittance across the coating of at least about 90%, a haze across the coating of no more than about 1% and a pattern that is approximately invisible under normal room lighting. 
     
     
         4 . The method of  claim 1  further comprising rinsing the coating after a desired time following application of the fusing solution. 
     
     
         5 . The method of  claim 1  further comprising applying a polymer overcoat to the patterned differentially conductive coating. 
     
     
         6 . The method of  claim 1  wherein the fusing agent is selected from halide anions, a reducing agent combined with a metal ion source and an alkaline agent in an effective amount, or a combination thereof. 
     
     
         7 . The method of  claim 1  wherein the fused metal nanostructured layer comprises nanowire segments fused into the network with an average diameter of no more than about 40 nm. 
     
     
         8 . The method of  claim 1  wherein the crosslinked polymer comprises a polyurethane, acrylic resin, acrylic copolymer, cellulose or mixture thereof. 
     
     
         9 . The method of  claim 1  wherein the fused metal nanostructured layer comprises silver and has a loading on the surface from about 0.5 mg/m 2  to about 200 mg/m 2 . 
     
     
         10 . The method of  claim 1  wherein the sheet resistance is no more than about 150 ohm/sq. 
     
     
         11 . The method of  claim 1  wherein the sheet resistance is no more than about 95 ohm/sq. 
     
     
         12 . The method of  claim 3  wherein the optical transmittance is at least about 94% and the haze is no more than about 0.9%. 
     
     
         13 . A method for the formation of a fused metal nanostructured network, the method comprising:
 depositing a fusing solution having an alkaline composition with a concentration of hydroxide anions of at least about 3×10 −5  M or a pH of at least about 9.5 pH units onto a layer of metal nanowires to fuse the metal nanowires.   
     
     
         14 . The method of  claim 13  wherein the fusing solution further comprises a metal salt. 
     
     
         15 . The method of  claim 13  wherein the concentration of hydroxide anions is at least about 1×10 −4  M or the pH is at least about 10 pH units. 
     
     
         16 . The method of  claim 13  wherein the fusing solution comprises an aqueous solvent. 
     
     
         17 . The method of  claim 13  wherein the fusing solution comprises an alcohol solvent. 
     
     
         18 . The method of  claim 13  wherein the layer of metal nanowires has a loading on a substrate surface from about 0.5 mg/m 2  to about 200 mg/m 2 . 
     
     
         19 . The method of  claim 13  wherein the metal nanowires are fused to form a fused metal nanostructured network having an electrical conductivity of no more than about 300 ohm/sq, a transmittance of at least about 90% and a haze of no more than about 1.1%.